Question

The energies of an electron in the first orbit of $H{e}^{+}$ and in the third orbit of $L{i}^{2+}$ in joule are respectively:

• A. $-8.72\times {10}^{-18},-2.18\times {10}^{-18}$
• B. $-8.72\times {10}^{-18},-1.96\times {10}^{-17}$
• C. $-1.96\times {10}^{-17},-2.18\times {10}^{-18}$
• D. $-8.72\times {10}^{-17},-1.96\times {10}^{-17}$

Answer 1

The correct option is A $-8.72\times {10}^{-18},-2.18\times {10}^{-18}$

$Energyofanelectronin{n}^{th}orbit$
$ofhydrogenlikespecies=-2.18\times {10}^{-18}\frac{Z^2}{n^2}$
where Z is atomic number.
For $H{e}^{+}\to$
$E_n=-2.18\times {10}^{-18}\frac{2^2}{1^2}=-8.7\times {10}^{-18}J$
For $L{i}^{2+}\to$
$E_n=-2.18\times {10}^{-18}\frac{3^2}{3^2}=-2.18\times {10}^{-18}J$